A KeyDrive is basically a bit of flash memory with a USB interface. They're roughly as large as a thumb (so sometimes referred to as "thumb drive") and perfect for carrying one around on your keychain (hence the name "key drive"). Their capacity is commonly 128MB, which makes them a more sensible contemporary means of transporting data than FloppyDisks would be. Such data could be your various PrivateKeys (for SSH, GPG, etc) so you never need to store them on a HardDisk. You can even boot from a KeyDrive if your BIOS supports this. Some LinuxDistributions are bootable directly from a KeyDrive, others can use a KeyDrive to make your home directory and other configuration data persistent.